A low-voltage device such as a lamp, a small household appliance etc. requires a power supply or “driver” for converting mains power into appropriate voltage and current for the device. For example, an LED light source can be driven from a power supply that converts the mains AC power into a DC output at a suitable level. Without protective measures being taken, a component failure somewhere in the circuit might result in an excessive voltage and/or current at some point, which can present a fire hazard or might put the user at risk from electric shock. Therefore, such drivers are generally constructed so that a primary side (connected to the mains) is isolated or separated from a secondary side (connected to the load). Such an isolated driver is also referred to as a mains-separated driver. To ensure safety, an isolated driver or power supply must ensure that the output voltage and current levels do not exceed a certain threshold. For example, the Underwriters Laboratories standard UL 1310 is directed at Class 2 power units for indoor and outdoor use. To obtain UL 1310 class 2 certification, a power supply or driver must ensure that its output voltage never exceeds 60 V, its output current never exceeds 2.5 A; and its output power never exceeds 100 W. These requirements must be fulfilled at all times during operation of the power supply or driver, even if a component of the overall circuit has failed. Therefore, manufacturers of such power supplies or drivers generally include some kind of protection circuit that isolates the secondary side of the driver from the primary side.
However, the prior art solutions are generally complex and require many components, thus adding to the design effort and the cost of the power supply product. In addition some fault situations may not be detected by and the driver cannot be considered fully compliant. As example of prior art, the man of the art can consult U.S. Pat. No. 8,520,415 or EP2284980 or US2014/0328427.
Therefore, it is an object of the invention to provide a more economical way of ensuring that the output of an isolated driver of the type described above remains within safety levels at all times during operation.